EXPERIMENTS ON CLEAVAGE 255 
into normal sea-water, I found that the manner of segmenta- 
tion changes in a remarkable way, according to the time the 
eggs had been in the concentrated sea-water. 
3. I fertilized eggs of sea-urchins at 9:30 in the morn- 
ing, and at 9:43 a part of these eggs were put into sea-water 
to which 2 g. of NaCl to 100 c.c. had been added. The rest 
of the eggs remained in normal sea-water. I will call the 
sea-water to which 2 g. of NaCl to 100 c.c. had been added 
the concentrated solution, and the eggs which had been 
exposed to it the plasmolyzed eggs. At 10:20, before any 
segmentation even in the normal sea-water had taken place, 
I took a lot of eggs out of the concentrated solution and 
brought them back into normal sea-water. At 10:33 these 
eggs began to segment. The segmentation was a normal 
one, as only segmentation into two cells took place. At the 
same time segmentation had taken place in nearly all of the 
normal eggs. The only difference between the normal eggs 
and the plasmolyzed eggs was that the former at 10:33 were 
nearly all segmented, while of the latter only a small part had 
undergone segmentation. Ten minutes later, however, every 
second one of the plasmolyzed eggs was segmented, mostly 
into two, exceptionally into four, segments. But now the 
situation began to change. By this time the normal eggs 
began to reach the four-cell stage, and now many of the 
plasmolyzed eggs which had not yet segmented into two cells 
began to segment into three or four cells at once, without 
going through the two-cell stage at all. The cleavage took 
place in this way, that at the same time, or shortly after each 
other, spherical projections appeared on the surface of the 
egg, which at first were coherent, but which soon, at the same 
time or in quick succession, were separated. This kind of 
segmentation seems to be identical with that which O. and 
R. Hertwig observed under other circumstances, and have 
described as Knospenfurchung.’ The further segmentation 
10, AND R. Hertwia, Jenaische Zeitschrift, Vol. XX (1887). 
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